[POWERPC] Remove old dcr.S

When I renamed dcr.S to dcr_low.S (and added dcr.c) it looks like the
old dcr.S file didn't properly get removed.  This fixes it.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>